Dehydrocyclodimerization of low molecular weight paraffins



United States Patent 6 f corporation of Delaware No Drawing. Filed Apr. 5, 1966, Ser. No. 540,187

8 Claims. (Cl. 260-673) This application is a continuation-impart of copending application Serial No. 218,099, filed August 20, 1962.

This invention relates to the conversion of paraffin hydrocarbons, and, more particularly, to the dehydrocyclodimerization of low molecular weight paraffins to produce higher molecular weight aromatic hydrocarbons.

The present invention is directed to a process for producing aromatic hydrocarbons and hydrogen, and comprises contacting at least one parafiin hydrocarbon containing 3 to 5 carbon atoms per molecule with a catalyst comprising at least one member selected from the group consisting of Group VIII metals and compounds thereof, disposed on a solid, alumina-containing support at a temperature of from about 800 to 1200 F. and a pressure of from about 2 to 1500 p.s.i.a. The acidity of the alumina containing support must be such that the Acidity Index (to be defined below) of the entire catalyst is between and 9.

It has been found that if the described reaction conditions and catalysts are employed in the subject process, the specified C to C paratiins will be converted to substantial yields of hydrogen and aromatic hydrocarbons containing more carbon atoms than that of any hydrocarbon component of the parafiin feed. It is apparent that this result is quite different from the well-known dehydrocyclization reaction wherein higher boiling paraffins, e.g., heptane and octane, are converted to cyclic compounds containing the same number or less carbon atoms in the molecule than those in the feed. Thus, the present reaction can be termed dehydrocyclodimerization to distinguish it from conventional dehydrocyclization.

As noted, paraflins containing 3 to 5 carbon atoms per molecule are converted to aromatics by the present process. Thus, propane, normal butane, isobutane, normal pentane and the isomeric pentanes, or mixtures thereof, can be employed. It is preferred to use the butanes as the feed to the process.

Suitable catalysts for the reaction comprise Group VIII metals disposed on a solid, alumina-containing support. Of these metals, the noble metals are preferred. Still more preferred are platinum and/ or palladium. Generally, the total amount of Group VIII metals on the catalyst should be in excess of 0.3 weight percent (as the metal) of the entire catalyst. The amount preferably lies in the range of from about 0.5 to 10.0 weight percent, and even more preferably, from about 0.6 to 3.0 weight percent.

The catalyst support can be alumina alone, as long as the acidity index of the entire catalyst is between 0 and 9. Alumina is generally considered to possess intrinsic acidity. However, incorporation onto the alumina of small amounts of basic components, such as alkali metals, is effective in poinsoning the acidity. For example, it can be shown (see Pines, H. and Haag, W., J. Am. Chem. Soc., 82, 247 1 (1960)) that less than about 1.0 weight percent sodium is effective in completely neutralizing all the acidic sites on an alumina catalyst. Therefore, alumina containing alkali metals in significant amounts, as for example, greater than 1.0 percent by weight, will not possess suflicient acidity to give the overall catalyst composition an acidity index between 0 and 9.,

3,296,324 Patented: J air. 3', 7

Preferably, additional acidity is imparted to the support, and, hence, to the catalyst. This can be accomplished in a number of ways. For example, an alumina containing catalyst can be increased in acidity by the inclusion of halogens in the catalysts such as chlorides and/or fluorides. Furthermore, the catalyst can be in creased in acidity by employing a support comprising both alumina and silica. Acid-activated clays and synthetic metal aluminum silicates (including synthetic zeolitic aluminos icates normally referred to as molecular sieves) cL. alSO be employed with alumina as the catalyst support.

For purposes of this invention, it is necessary that the catalyst have an acidity index less than 9. The acidity index is determined as follows. A sample of catalyst is placed in a reactor at 1040 F. and either normal butane or isobutane at atmospheric pressure and a liquid hourly space velocity (LHSV) of 1 volume of feed per 'volume of catalyst is contacted with the catalyst. A sample of the product is withdrawn after 10 minutes have elapsed from the start of the run, and the butenes in the product are measured. The mole ratio of isobutene to normal butenes is then determined. Depending on the feed used, the acidity index is defined and determined (1) Using a normal butane feed moles normal ut-e e moles isobutene (2) Using an isobutane feed 019 =ac1d1ty index The value, 0.79, is the equilibrium ratio of isobutene to normal butenes in the butane conversion reaction, based on the data of F. D. Rossini et al., Selected Values of Physical and Thermodynamic Properties of Hydrocarbons and Related Compounds, American Petroleum Institute Research Project 44, Carnegie Press, Pittsburgh, Pennsylvania (1953).

The acidity index is in terms of an approach to equilibrium between isobutene and the normal butenes. The more acidic the catalyst, the closer the mole ratio of isobutene to normal butenes in the products will approach the equilibrium value. Consequently, the more acidic the catalyst, the smaller its acidity index will be, and in general the greater the conversion of the feed comprising low molecular weight paraffins to higher molecular weight aromatic hydrocarbons will be. It is preferred to use a catalyst which has an acidity index below 5.0, and more preferably below 3.0. All of the catalysts discussed in this specification as being useful for purposes of the present invention have acidity indices within the preferred range.

The present process is conducted at temperatures in the range of from about 800 to 1200 F., and preferably from about 950 to 1100 F. Pressures may be subat mospheric, atmospheric or superatmospheric and will fall in the range of from about 2 to 1500 p.s.i.a. The parafliu feed can be introduced to the reaction zone at a liquid hourly space velocity (LHSV) of from about 0.1 to 30 or even higher, as either a liquid, vapor, or in a mixed liquid-vapor phase. The reaction itself is conducted in the vapor phase. Hydrogen can be passed along with the feed into the reactor, but it is preferred that the mole ratio of hydrogen added to the reactor (other than that produced in the reaction). to the paraifin hydrocarbon feed is less than 1.0, and more preferably is less than 2 moles of hydrogen to 3 moles of hydrocarbon.

It has been found that higher aromatic yields result when essentially no hydrogen (other than that produced in the reaction) is added. Because of the rather large production of hydrogen, it may be desirable to pass an inert gas such as helium or nitrogen into the reaction zone along with the paraflins so as to reduce the hydrogen partial pressure within the reaction zone. Also, hydrogen sulfide or compounds capable of forming hydrogen sulfide within the reactor (as by decomposition) can often be advantageously employed as a feed component so as to reduce catalyst fouling due to coke formation.

Example 1.-A number of experimental runs were made on the conversion of essentially pure isobutane to produce aromatic hydrocarbons utilizing a number of catalysts and varying reaction conditions. This feed was selected to emphatically show the nature of the dehydrocyclodimerization reaction and the high yields obtainable with the particular catalysts.

A number of diflerent catalysts, all of which comprised platinum metal disposed on alumina supports, were employed in these runs. In addition, these catalysts contained halides. Table I summarizes the platinum and halide content of the catalysts used.

The results of the runs, along with the reaction conditions, are shown in Table II. No hydrogen was added to the reactor in the course of the runs, except where 40 4 In the Table H summarized runs, large amounts of hydrogen were produced. For example, in Run No. 7, about 0.9 mole of hydrogen were formed per mole of feed. The amount of hydrogen produced in the other.

experiments varied due to the differences in overall conversion and product distribution.

From the data presented in Table II, a number of.

observations can be made.

With respect to temperature, it can be 'seen that par-,

ticularly high yields were obtainable at reaction tempera 10 tures in the 1000 to 1100 F. range. A comparison of runs 3 and 4 shows that, under essentially the same conditions and with the same catalyst, adding substantial amounts of hydrogen to the feed was operable, butnot particularly desirable. Runs 7 to 11, conducted at the same temperature and pressure but with four different catalysts, show that very high yields were attained by using the catalysts having increased acidity as a result of halide addition. Run 12, conducted under the same conditions as Runs 7 to-ll, did not have such high yields,

of isobutane to produce aromatic hydrocarbons utilizing each of the various catalysts was performed under contions of temperature, pressure and space velocity such that the acidity index of each catalyst could be determined. The reaction conditions were a temperature of 1040 F.,

a pressure of 14.7 p.s.i.a. and a liquid hourly space velocity of 1.0 No hydrogen was added to the reactor during the course of the run.

Table HI presents the results of the runs as Well as 1 the compositions of the catalyst.

It is noted that the acidity indices of the catalysts used noted. 1n this example all he wlthin the preferred hmits. The TABLE II Run No 1 2 3 4 5 6 7 8 9 10 11 12 Catalyst E E E E E E E E A B C D Temperature, F 900 1, 110 997 980 1, 000 1, 100 1, 040 1, 040 1, 040 1, 040 1, 040 1, 040 Pressure, p.s.1.a 14. 7 14. 7 115 115 l, 234 14. 7 l4 7 4. 7 14. 7 14. 7 14. 7 Hydrogen/Hydrocarbon Mol Ratio. 0. 63 Helium/Hydrocarbon Mol Ratio- 0. 55 LHSV 2. 5 2 54 6. 84 6. 84 1. 0 8. 0 2. 5 2. 6 1. 05 1. 03 2. 64 2. 4 Hydrocarbon Products, wt. percent of total:

Unreacted Isobutane 51. 2 48. 3O 36. 30 47. 00 16. 60 24. 17. 02 22. 60 23. 10 10. 50 40. 00 33. 70 Methane v 1. 0 4. 05 5. 52 1. 20 6. 83 10. 40 5. 74 3. 52 9. 20 7. 16 7. 5. 27 C, Hydrocarbons O. 5 3 10 2. 12 1. 40 18. 80 8. 50 2. 98 3. 30 7. 72 7. 46 4. 56 2. 40 C Hydrocarbons- 2. 4 2 90 13. 40 3. 85 28. 90 16. 00 12. 00 10. 00 12. 80 14. 70 7. 73 9. n-Butane 21. 0 2 90 37. 10 32. 10. 00 29. 00 16. 02 15. 80 9. 00 14. 25 6. 14 7. Isobutene 14. 0 10. 60 1. 93 5. 00 1. 7O 1. 54 12. 40 11. 90 8. 60 8. 08 7. 40 28. n-Butenes and Butadiene 5. 7 14 20 1. 57 3. 1 24 0.65 14. 18 13.81 9. 31 11. 46 8. 97 8. C -C Aliphatics 1. 0 0. 36 0. 51 1. 29 8 81 0. 22 0. 46 0.42 0.37 0. 25 0. 25 0. Benzene 0. 1 2. 08 0. 11 0. 37 1 74 0. 1. 33 1. 40 2. 44 2. 40 2. 22 0. To1uene 0. 7 3. 15 0. 57 1. 39 3 10 2. 03 4 38 3.88 5. 18 6. 40 4 75 1. Ca Aromatics 2. 0 4. 79 0. 87 2 20 2 28 3. 36 12. 71 11 45 9. 16 15.00 7 87 2. 0 -0 0 Aromatics O. 4 0. 25 0. 46 0. 78 1 92 3. 12 2. 34 2 56 0. Coke (if included in analysis) 3. 32 2. 59 Total Aromatics, wt. percent of Isobutane converted to gas and liquid products. 6 5 19. 9 2. 4 7. 4 8. 6 8. 7 23 1 24. 1 25. 9 29 2 29 0 6 7 TABLE III Run No 13 14 15 16 17 I 18 I 19 I 20 I 21 22 Catalyst:

Platinum content, wt. percent- 0. 8 0. 315 0. 75 0. 75 0. 74 0. 86 0. 66 0. 5 0. 9 0. 8 Chloride content, wt. percent- 0. 83 0. 49 0 0. 77 0. 54 0. 02 0. 64 0. 5 0 81 0. 61

. 5 Reaction Resu1ts:

Unreacted feed, wt. percent 24. 4 43.6 15- 3 6. 7 17. 3 10 17. 9 5. 8 18. 7 Total aromatics, wt. percent 24 9 15. 7 21. 0 34 21. 4 22 22. 7 24. 6 10. 7 Isobutene/normal butenes mole ratio- 0 81 0. 85 1. 0 0. 78 0. 74 1. 23 0. 81 0.85 0. 9 1. 7 Acidity index 0. 02 0. 06 0. 21 0 0 0.44 0 02 0. 06 0. 11 0. 91

due to the fact that Catalyst D did not have additional acidity imparted to it by significant halide addition (Cata-.

These catalysts contained catalysts used in Runs 16 and 17 show acidity indices of 0. Straightforward computation of the acidity indices would have given negative numbers for these two catalysts but since it is theoretically impossible for the isobutene/ 6 Using a normal butane feed, the acidity indices of the catalysts are well within the preferred limits for purposes of this invention.

Example 5.Four additional catalysts, all employing normal butel1e q ratio to go fh qquhibfium 5 Group VIII metals disposed on commercial alumina sup- Value when 115mg lsobutahe feed, the acldlty mdlces are ports were prepared and used as catalysts in the dehydrog as A f 1 d cyclodimerization reaction of the present invention. A senes o ig fg fif g 6 normal butane feed was contacted with the catalysts. Two m w w u mm con W van ca ys of the runs (Runs 34 and 35) were conducted under reacau of whlch compnsed Platmum metal dlsposed on tion conditions such that the a idit i dice co ld b det alumina supports. In addition, two of the catalysts cond Th th t y 5: 2 e tained small amounts of potassium. The reaction conmine e 0 er W0 runs uns an f were ditions were controlled in order to measure the acidity dhcted Pressures (22's and P F indices of the catalysts; that is, a temperature of 1040 l greater than hq Wh n de ermining ac dity F a pressure f p513 and an LHSV f L0 wem 15 indices; hence the acidity indices were not determined. used. No hydrogen was added to the reactor during the N0 hydrogen Was added to the reactor during the runs; runs, T bl IV ma i th o iti n f th ow, The compositions of the catalysts as well as the results of lysts used and the results of the runs. the runs are presented in Table VI.

TABLE IV Run N0 23 24 25 26 27 Catalyst:

Platinum Content, Wt. Percent 0.8 0. 5 0. 58 0.98 0.90 Chloride Content, Wt. Percent U 0 0 0 1.03 Potassium Content, Wt. Percent 0 0 0 3. 78 3. 78 Reaction Results;

Um'eacted Feed, Wt. Percent 18. 4 43. 5 18. 6 72. 4 93. 6 Total Aromatics, Wt. Percent 15.5 12.0 19. 2 0. 9 0. 13 Isobutene/Normal Butenes Mole Ratio 2. 8 1. 64 1. 5 38 26 Acidity Index 1.51 0.85 0.71 37.2 25.2

The catalysts containing platinum metal on alumina TABLE VI supports and having no chloride or potassium present (Runs 23, 24 and 25) display acidity indices well within Run N0 32 33 34 35 the preferred range of O to 3. The catalysts containing platinum and potassium on alumina supports (Runs 26 Catalyst; and 27) display acidity indices well above the limits re- Metahcvntentiwt- Percent 2 -0 -8 ChldCt,. quired as part of this invention. Note, too, the low aroif $3.55,}, fl fiifii None 1 0 None None matic yields which resulted in Runs 26 and 27. The small Unreacted n-Butime 6 Methane 5. 2 5. 5 5. 2 2. 4 amount of added potassium effectively neutralized the g fiydro arb g; 7 22 50 4,0 ropane 8 1.9 0.6 acidity of the alumina supports and made the catalysts un Isobutane and Propy1ene 6' 9 6 8 5'1 5 4 acceptable for dehydrocyclodinierization of low molecular Isobntene 4.1 2. 7 2,1 1.3 n-Buteues and Butadiene 9. 2 4. 6 4. 0 2. 2 weight paraifins to produce higher molecular weight aro Grog Aliphatics u 0. 6 0. 5 0. 2 0. 2 matic hydrocarbons. Even the addition of chloride to a p y L3 20 L9 o5 ouene 2.3 3.8 2.7 1.0 catalyst containingpotassium (Run 27) was ineffect vein Cs Aromaticsun Z 1 3.9 3' 0 L 0 restoring the acidity necessary for purposes of this in- C9-C oA10maticS" 0.2 0.3 1.5 1.0 venfion Y Coke 7. 7 4. 4 s. 1 1. 9 Hydrogen 1. 5 1. 0 1. 5 0. 4 Example 4.-Using normal butane as a feed, a number Total Aromatics, Wt. Percent of of experimental runs were made using catalysts containing flgyg giggggffsf fji jef 12 5 m 4 2L 6 16. 0 platinum and chloride on alumina supports. Again the g fi m Butenes M019 45 59 =3 59 reaction conditions were maintained such that the acidity Acidit ind}; :5 indices could be determined. The temperature was maintained at 1040 F., the pressure at 14.7 p.s.i.a., and the nhodiuni. Palladium. Nickel. LHSV set at 1.0. No hydrogen was added to the reactor. 4 Ruthemum- 5 The results of the runs and the compositions of the cat- The above data show that the catalysts comprising alysts as well as the acidity indices are tabulated in 0 Group VIII metals on alumina supports are entirely satis- Table V. factory for purposes of this invention. The acidity indices all lie within the preferred range. Furthermore, the catalysts possess the appropriate acidity indices without addi- TABLE V tives (e.g., fluorides) incorporated onto the alumina sup- 5 ports to impart additional acidity to the catalysts.

In addition to the above experimental runs, aromatics N0 28 i 29 I 30 31 have been successfully produced from isobutane by employing a catalyst containing 1.7 percent (weight) pal- Catzil lrgttiznum Content Wt. Percent 075 [18 0.74 0.8 ladium, about 27.5 percent silica and about 70.8 percent Chloride Content, t- Percent-n 0- 77 0.8 6 M 9 alumina. Likewise, a catalyst containing 1.7 percent (by gif g f i Wt Percent 5 m8 215 4 weight) platinum, about 27 .5 percent silica and about 70.8 Total Aromatics glvg. tPercerlivti 14.8 17.6 4.8 percent alumina has been found to be suitable for use in ii i fl u ms 0. 64 0.7 0.57 0. as the pfffsent P Ac y Index- 16 76 During the reaction, some carbonaceous deposits (coke) are formed on the catalyst. The coke can be removed by catalyst bed, moving bed or fluid catalyst systems.

7 conventional methods, thereby regenerating the catalyst for reuse. .A plethora of patents (among them being US. Patents 2,641,582 and 2,664,404) describe various techniques for regenerating platinum and palladium catalysts. Generally, regeneration involves contacting the coked catalyst with dilute, oxygen-containing gases at temperatures sufiiciently high (700 to 1100 F.) to burn off the coke without damaging the catalyst surface area by sintering. Regeneration of a catalyst of the present invention has been done by contacting the catalyst (for example, Catalyst E, Example 1, described above) withan air-nitrogen mixture containing one to two percent oxygen at a temperature within the range of 700 to 900 F. These operations restored the catalyst to its original activity.

The present process can be conducted in either fixed Because of the coke laydown on the catalyst and the desirability of regenerating the catalyst, it is preferred to employ contacting systems wherein regeneration can be accomplished without discontinuing the flow of feed to the reaction zone or zones. This can be done in several ways. One method involves the use of a swing reactor. Such a unit comprises a plurality of fixed bed reaction zones with line manifolding so as to allow the feed to be passed into a first zone and when the catalyst in that zone is deactivated by coke, to shift the feed to a second freshly regenerated reaction zone. After shifting the feed to the second reactor, the deactivated catalyst in the first zone is regenerated and ready for use when the second reactor is deactivated.

Another preferred contacting system is one involving a fiuid catalyst system. 'In this operation, finely divided solid (fluid) catalysts are continuously recycled between a reaction zone and a separate regeneration zone. In each zone, the catalyst is maintained in a fluidized state that behaves much like a liquid. In the reactor, the feed is continuously contacted with freshly regenerated catalyst and the hydrocarbon products are removed from the reactor. The coked catalyst is continuously removed from the reactor and passed into the regenerator wherein it is contacted with an oxygen-containing gas to burn the coke and regenerate the catalyst. The regenerated catalyst is then returned to the reaction zone.

Whether employing a fixed, moving or fluid catalyst bed system, the hydrogen and hydrocarbons produced in the reaction zone are removed and recovered in any suitable manner, as by absorption and/or distillation. The actual separation of the various products can be done to suit the needs of the particular operator. Pref? erably, the C to C hydrocarbons recovered from the reaction zone are recycled thereto.

Iclaim:

1. A processfor converting low molecular weight parafiins to higher molecular weight aromatic hydrocarbons and hydrogen, which comprises contacting in a reaction zone at least one parafiin hydrocarbon containing from 8 3 to 5 carbon atoms per molecule witha catalyst comprising at least one Group VIII metal disposed on a solid,

alumina-containing support, said alumina support being of sufiicient acidity that the acidity index of the catalyst is between 0 and 9, at a temperature in the range of from about 800 to 1200 F., and at a pressure in the range of from about 2 to 1500 p.s.i.a., said contacting being done such that the mole ratio of hydrogen added 3 to said reactor (other than that produced in the reaction to said parafiin hydrocarbon is less than 1.0.

2. The process of claim 1, wherein the acidity index of the catalyst is between 0 and 5.

3 The process of claim 1, wherein the mole ratio of i hydrogen added to the reactor to paraflin hydrocarbon is less than 2 moles of hydrogen to 3 moles of hydrocarbon.

4 The process of claim 1, wherein the temperature,

is in the range of from about 950 to 1100 F.

5. The process of claim 1, wherein the paraffin hydrocarbon is contacted with the catalyst at a liquid hourly space velocity in the range of from about 0.1 to 3.0.

6. The process of claim 1 wherein the Group VIII metal is platinum.

7. The process of claim 1 wherein the Group VIII metal is palladium.

8. A process for converting low molecular weight paraffins to higher molecular weight aromatic hydrocarbons said alumina support being of suflicient acidity that the acidity index of the catalyst is between 0 and 9, at a temperature in the range of from about 800 to 1200 F.,

and at a pressure in the range of from about 2 to 1500 p.s.i.a., said contacting being done such that the mole ratio of hydrogen added to said paraffin hydrocarbon is less than 1.0, continuously recovering hydrogen and aromatic hydrocarbons from said reaction zone, contmuously withdrawing coke-containing catalyst from said reaction zone and regenerating said coke-containing cata lyst in a regeneration zone by contact with an oxygen-.

containing. gas at an elevated temperature, and contmuously returning regenerated catalyst from said regeneration zone to said reaction zone.

References Cited by the Applicant UNITED STATES PATENTS 2,900,427 8/1959 Viles. 2,992,283 7/1961 Eng. 3,000,809 9/1961 Ridgeway et al. 3,046,317 7/ 1962 Myers. 3,126,426 3/1964 Turnquest et a1.

ALPI-IONSO D. SULLIVAN, Primary Examiner. 

1. A PROCESS FOR CONVERTING LOW MOLEUCLAR WEIGHT PARAFFINS TO HIGHER MOLEUCLAR WEIGHT AROMATIC HYDROCARBONS AND HYDROGEN, WHICH COMPRISES CONTACTING IN A REACTION ZONE AT LEAST ONE PARAFFIN HYDROCARBON CONTAINING FROM 3 TO 5 CARBON ATOMS PER MOLECULE WITH A CATALYST COMPRISING AT LEAST ONE GROUP VIII METAL DISPOSED ON A SOLID, ALUMINA-CONTAINING SUPPORT, SAID ALUMINA SUPPORT BEING OF SUFFICIENT ACIDITY THAT THE ACIDITY INDEX OF THE CATALYST IS BETWEEN 0 AND 9, AT A TEMPERATURE IN THE RANGE OF FROM ABOUT 800 TO 1200*F., AND AT A PRESSURE IN THE RANGE OF FROM ABOUT 2 TO 1500 P.S.I.A., SAID CONTACTING BEING DONE SUCH THAT THE MOLE RATIO OF HYDROGEN ADDED TO SAID REACTOR (OTHER THAN THAT PRODUCED IN THE REACTION) TO SAID PARAFFIN HYDROCARBON IS LESS THAN 1.0. 